The present invention relates to a differential locking mechanism for locking (preventing) differential action in a final reduction gear of a vehicle.
In a conventional differential locking mechanism, a differential case rotating in a differential carrier and rotating shafts for transmitting rotation to right and left driving wheels (axle shafts or side gear shafts) are designed to be locked so as not to rotate relative to each other by using a spline type clutch means or a dog clutch means (see, for example, Japanese Utility Model Laid-Open Publications Nos. 58-89427 and 55-21264). The differential action is locked by preventing the differential case and the side gear shafts from rotating at different speeds. Further, a diaphragm device operated by engine intake manifold vacuum has been proposed as a means for providing the operating force for the differential locking mechanism (see Japanese Utility Model Laid-Open Publication No. 55-171636).
FIG. 4 shows an exemplary structure of a conventional differential locking mechanism. As shown in FIG. 4, each member constituting the differential locking mechanism is installed in a space 34 defined between a partition wall 36 and a side wall 1a of the differential carrier 1. Sleeve-like shaft support portions 2a, 2b integrally formed with or fixed on both sides of a differential case 2 are supported rotatably by the carrier 1 by side bearings 3, 3a in the differential carrier 1. The side bearing 3a (on right-hand side in FIG. 4) is faced by the partition wall 36.
The shaft support portion 2b extends from a bearing portion supported by the right side bearing 3a into the space 34. A spline piece 32 having external spline teeth 32a engages an outer circumference of the shaft support portion 2b in the space 34 so as to rotate with the shaft support portion 2b. The right side gear shaft 9 is formed integrally with a clutch hub 30 having external spline teeth 30a meshed with internal spline teeth 31a of a hub sleeve 31.
The sleeve 31 is formed with a groove for engagement with a fork 33. The fork 33 is fixed to a rod 35. Accordingly, when the rod 35 is moved to the left in FIG. 4, the sleeve 31 also is moved to the left by the fork 33. When the hub sleeve 31 is located in the position shown in FIG. 4, the internal spline teeth 31a mesh only with the external spline teeth 30a of the clutch hub 30, so that the side gear shaft 9 and differential case 2 can rotate at different speeds. Thus, differential action is allowed in this condition. However, when the hub sleeve 31 slides further to the left, the internal spline teeth 31a mesh not only with the external spline teeth 31a of the clutch hub 30, but also with the external spline teeth 32a of the spline piece 32. In this position, the side gear shaft 9 and differential case 2 are prevented from rotating at different speeds, so that the differential action is locked.
The above-mentioned conventional differential limiting mechanism has the following defects:
(1) As all the components of the differential limiting mechanism, that is, the clutch hub 30, hub sleeve 31, spline piece 32, fork 33, etc., are installed in the space 34 of the differential carrier 1, the differential carrier 1 itself must be rather large, and have a shape different from that of a conventional carrier, requiring a new die for molding the carrier 1 and a machining line therefor.
(2) As the shaft support portion 2b of the differential case 2 extends into the space 34, the rear opening portion of the carrier 1 for installing the differential case 2 into the differential carrier 1 must be enlarged, reducing the rigidity of the rear opening portion of the carrier 1 and the sealability between the carrier 1 and a rear cover (not shown).
(3) As the spline piece 32 is connected to the outer circumference of the extended portion of the shaft support portion 2b, a through-hole 36a must be formed to allow for installation of the spline piece 32 through the partition wall 36 separating the differential carrier 1 from the space 34, which reduces the axial support rigidity of the side bearing 3a. Further, upon installing the differential case 2 into the carrier 1, a preload adjusting shim 24 interposed between an outer race of the side bearing 3a and the partition wall 36 must be installed preliminarily at an outer circumference of the extended portion of the shaft support portion 2b, which makes installation of the shim 24 difficult.
(4) If a higher strength differential locking mechanism is required, it is necessary to mold a differential carrier 1 having a larger capacity for the sole purpose of meeting such requirement.